Marko Cetina

Observation of Cold Collisions between Trapped Ions and Trapped Atoms

We study cold collisions between trapped ions and trapped atoms in the semiclassical (Langevin) regime. Using Yb+ ions confined in a Paul trap and Yb atoms in a magneto-optical trap, we investigate charge-exchange collisions of several isotopes over three decades of collision energies down to 3 mueV (k_{B}x35 mK). The minimum measured rate coefficient of 6x10;{-10} cm;{3} s;{-1} is in good agreement with that derived from a Langevin model for an atomic polarizability of 143 a.u.

Micromotion-Induced Limit to Atom-Ion Sympathetic Cooling in Paul Traps

We present, and derive analytic expressions for, a fundamental limit to the sympathetic cooling of ions in radio-frequency traps using cold atoms. The limit arises from the work done by the trap electric field during a long-range ion-atom collision and applies even to cooling by a zero-temperature atomic gas in a perfectly compensated trap. We conclude that in current experimental implementations, this collisional heating prevents access to the regimes of single-partial-wave atom-ion interaction or quantized ion motion. We determine conditions on the atom-ion mass ratio and on the trap parameters for reaching the s-wave collision regime and the trap ground state.

Interaction between Atomic Ensembles and Optical Resonators: Classical Description

Abstract Many effects in the interaction between atoms and a cavity that are usually described in quantum mechanical terms (cavity quantum electrodynamics, cavity QED) can be understood and quantitatively analyzed within a classical framework. We adopt such a classical picture of a radiating dipole oscillator to derive explicit expressions for the coupling of single atoms and atomic ensembles to Gaussian modes in free space and in an optical resonator. The cooperativity parameter of cavity QED is shown to play a central role and is given a geometrical interpretation. The classical analysis yields transparent, intuitive results that are useful for analyzing applications of cavity QED such as atom detection and counting, cavity cooling, cavity spin squeezing, cavity spin optomechanics, or phase transitions associated with the self-organization of the ensemble-light system.

Ultrafast many-body interferometry of impurities coupled to a Fermi sea

Sluggish turmoil in the Fermi sea The nonequilibrium dynamics of many-body quantum systems are tricky to study experimentally or theoretically. As an experimental setting, dilute atomic gases offer an advantage over electrons in metals. In this environment, the heavier atoms make collective processes that involve the entire Fermi sea occur at the sluggish time scale of microseconds. Cetina et al. studied these dynamics by using a small cloud of 40K atoms that was positioned at the center of a far larger 6Li cloud. Controlling the interactions between K and Li atoms enabled a detailed look into the formation of quasiparticles associated with K “impurity” atoms. Science, this issue p. 96 Precise manipulation of interactions between impurity and majority atoms gives insight into polaron formation. The fastest possible collective response of a quantum many-body system is related to its excitations at the highest possible energy. In condensed matter systems, the time scale for such “ultrafast” processes is typically set by the Fermi energy. Taking advantage of fast and precise control of interactions between ultracold atoms, we observed nonequilibrium dynamics of impurities coupled to an atomic Fermi sea. Our interferometric measurements track the nonperturbative quantum evolution of a fermionic many-body system, revealing in real time the formation dynamics of quasi-particles and the quantum interference between attractive and repulsive states throughout the full depth of the Fermi sea. Ultrafast time-domain methods applied to strongly interacting quantum gases enable the study of the dynamics of quantum matter under extreme nonequilibrium conditions.

Bright source of cold ions for surface-electrode traps

We produce large numbers of low-energy ions by photoionization of laser-cooled atoms inside a surface-electrode-based Paul trap. The isotope-selective traps loading rate of 4x10{sup 5} Yb{sup +} ions/s exceeds that attained by photoionization (electron-impact ionization) of an atomic beam by three (six) orders of magnitude. Traps as shallow as 0.13 eV are easily loaded with this technique. The ions are confined in the same spatial region as the laser-cooled atoms, which will allow the experimental investigation of interactions between cold ions and cold atoms or Bose-Einstein condensates.

Influence of grating parameters on the linewidths of external-cavity diode lasers

We investigate experimentally the influence of the grating reflectivity, grating resolution, and diode facet antireflection (AR) coating on the intrinsic linewidth of an external-cavity diode laser built with a diffraction grating in a Littrow configuration. Grating lasers at 399, 780, and 852 nm are determined to have typical linewidths between 250 and 600 kHz from measurements of their frequency noise power spectral densities. The linewidths are little affected by the presence of an AR coating on the diode facet but narrow as the grating reflectivity and grating resolution are increased, with the resolution exerting a greater effect. We also use frequency noise measurements to characterize a laser mount with improved mechanical stability.

Chapter 4 – Interaction between Atomic Ensembles and Optical Resonators: Classical Description

Abstract Many effects in the interaction between atoms and a cavity that are usually described in quantum mechanical terms (cavity quantum electrodynamics, cavity QED) can be understood and quantitatively analyzed within a classical framework. We adopt such a classical picture of a radiating dipole oscillator to derive explicit expressions for the coupling of single atoms and atomic ensembles to Gaussian modes in free space and in an optical resonator. The cooperativity parameter of cavity QED is shown to play a central role and is given a geometrical interpretation. The classical analysis yields transparent, intuitive results that are useful for analyzing applications of cavity QED such as atom detection and counting, cavity cooling, cavity spin squeezing, cavity spin optomechanics, or phase transitions associated with the self-organization of the ensemble-light system.

Laser cooling of trapped ytterbium ions with an ultraviolet diode laser

We demonstrate an ultraviolet diode laser system for cooling of trapped ytterbium ions. The laser power and linewidth are comparable to those of previous systems based on resonant frequency doubling, but the system is simpler, more robust, and less expensive. We use the laser system to cool small numbers of ytterbium ions confined in a linear Paul trap. From the observed spectra, we deduce final temperatures of < 270 mK.

Suppression of ion transport due to long-lived subwavelength localization by an optical lattice.

We report the localization of an ion by a one-dimensional optical lattice in the presence of an applied external force. The ion is confined radially by a radio frequency trap and axially by a combined electrostatic and optical-lattice potential. Using a resolved Raman sideband technique, one or several ions are cooled to a mean vibrational number =(0.1±0.1) along the optical lattice. We measure the average position of a periodically driven ion with a resolution down to λ/40, and demonstrate localization to a single lattice site for up to 10 ms. This opens new possibilities for studying many-body systems with long-range interactions in periodic potentials, as well as fundamental models of friction.

One-dimensional array of ion chains coupled to an optical cavity

We present a novel system where an optical cavity is integrated with amicrofabricatedplanar-electrode iontrap.The trapelectrodesproduceatunable periodic potential allowing the trapping of up to 50 separate ion chains aligned with the cavity and spaced by 160µm in a one-dimensional array along the cavity axis. Each chain can contain up to 20 individually addressable Yb + ions coupled to the cavity mode. We demonstrate deterministic distribution of ions between the sites of the electrostatic periodic potential and control of the ion-cavity coupling. The measured strength of this coupling should allow access to the strong collective coupling regime with .10 ions. The optical cavity could serve as a quantum information bus between ions or be used to generate a strong wavelength-scale periodic optical potential.